This invention relates generally to well completion methods and more particularly to methods of defining fracturing treatments for oil or gas wells.
In completing an oil or gas well after the wellbore has been drilled, a procedure referred to as xe2x80x9cfracturingxe2x80x9d may be performed to enhance the productivity of the well. Fracturing in essence creates in the oil or gas-bearing formation an enhanced conductive path through which the oil or gas can flow more readily than through the unfractured formation rock itself.
Although fracturing may increase oil or gas flow from the formation into the wellbore, achieving this result may not be economically efficient if the cost of fracturing is more than the revenue that will be obtained from the increased production. Even if a fracturing process is economical for a particular well, the design of the fracturing job should be carefully made to ensure its success. The advent of the Three Dimensional Fracture Simulators (3-D) has helped optimize fracture treatments by predicting fracture growth in height. This has shown that many times the fracture grows out of the desired formation and thus reduces the effectiveness of the fracture treatment. This 3-D growth is key to fracture optimization and can be used to determine when the fracturing process is no longer achieving the fracture length growth and thus reducing the economic impact of the treatment.
A traditional way of creating a fracturing treatment design has depended upon the ability of a skilled person to select a fracturing fluid with which to hydraulically fracture the formation and a proppant which is to be carried into the fracture by the fracturing fluid and left there to prop the fracture open after the hydraulic pressure is released. The details and quality of a particular design of such a fluid system have depended upon the knowledge and experience of this person. Typically, that knowledge and experience are applied to select a fracturing fluid and proppant with whatever factors the individual designer has come to rely on. Maybe more than one such design is conceived, and maybe the designs are tested in a fracture modeling simulator to see what the simulator projects will be the resultant fracture for each of the designs. Economic analyses can be made for the various simulations using, for example, return on investment (ROI) or net present value (NPV) from a reservoir simulation of production results from each proposed treatment and cost of the treatment. From these cost versus production analyses, one of the designs is selected and used in controlling the pumping of the selected fracturing fluid and proppant into the well. If the skilled individual is at the well site during the fracturing treatment or otherwise in real-time communication, changes to the design might be made xe2x80x9con-the-flyxe2x80x9d based on conditions that are monitored during the fracturing job.
One shortcoming of the aforementioned traditional technique for designing a fracturing job is that it significantly depends on the individual skill of the person who is designing the treatment schedule for the job. Thus, each fracturing job to be performed in this manner depends on the availability and ability of a particular person. This limits the design by a person""s own shortcomings, and it hinders the transfer of knowledge gained from one area/formation into other areas or formations. This approach does not necessarily mean that the xe2x80x9coptimumxe2x80x9d fracturing treatment has been designed and delivered. One has to realize that the optimum treatment does not necessarily mean the largest. This type of approach also can provide a myriad of different possible designs to be analyzed by the simulator and economic factors.
In view of at least the foregoing shortcomings, there is a need in the well completion field, and specifically the fracture treatment design field, to reduce the dependency on specific individuals with unique knowledge, experience and ability; however, there is also the need to make such expertise more widely available so that it can be used consistently for more wells. There is also the need for a design technique that more easily arrives at one or more possible solutions than may be required for a human to directly create such design. There is also the need to arrive at possible fracturing treatment solutions based on actual well data and consistent, predetermined analytical factors. There is also the need to provide the ability to optimize a design, including economic optimization. Towards this goal we need to apply the knowledge gained through theory in a practical fashion reaching the right mix of sound fundamental work and field gained experience.
The present invention overcomes the above-noted and other shortcomings of the prior art and meets the aforementioned needs by providing a novel and improved optimization process for well completions in general and for fracturing treatments in particular. This process is to optimize the materials used (fluid, proppant, breakers, etc.) in the fracturing treatment as well as the height, length and width of the fracture to achieve the optimized fracture treatment based on the desired economic drivers. The stresses within the oil or gas bearing formation as well as the surrounding formations control the geometry of the fracture created. These stresses will determine the geometry of the fracture and can be modeled in a 3-D fracture simulator (FracPro(copyright), FracProPT(trademark), StimPlan(trademark), M-Frac(trademark), etc.) and this geometry is key to optimizing the fracture treatment.
Instead of starting with various fracturing materials based on some individual""s personal knowledge or preferences and running simulations and economic analyses to project possible resulting production and cost, the present invention starts by determining a conductivity profile (preferably an optimum one) for the given reservoir to be fractured. Once the conductivity profile, for a constant pressure drop down the fracture, is determined for the given reservoir conditions, along with any other losses like multi-phase flow or gel damage, the materials needed to obtain this conductivity profile are determined by the respective material""s performance and economics. The materials selected are based on their ability to meet the conductivity objective and their rank based on economic value to the fracture conductivity objective (for example, proppant judged on strength and cost/conductivity for given reservoir conditions, stress, temperature, etc.). In this way unsuitable materials are eliminated early in the analysis so that the materials to evaluate in the desired design are only those capable of achieving the final conductivity goal in an economical manner. Whereas a prior approach might result in a very large number of combinations of materials to evaluate to achieve the desired results by trial and error, the new approach of the present invention significantly reduces the combinations of materials for the design process and ensures that the materials in the evaluation process are only those that should be considered for the reservoir conditions. This ensures that the final simulations use the technically appropriate materials and are the best value materials for the desired conductivity objectives. The theoretical length desired for the formation to be stimulated should be verified by 3-D simulation for height, length and width before the appropriate materials are selected and the preferably optimized fracture geometry determined.
Adding a further step in the new approach of the present invention gives the designer a pumping schedule to be performed on the surface after an initial test in the actual well. This differs from the old approach in which a pumping schedule is first prepared and pumping of the job begun and then evaluated as to how close the pumping schedule comes to producing the desired conductivity profile needed for the reservoir conditions. Waiting until after a test is run on the actual well to provide a pumping schedule as done in the present invention is a significant change because changes in assumptions may need to be made after test data is obtained from the well, such as data from a mini-frac process. When the mini-frac data is matched in the 3-D fracture simulator by changes in reservoir parameters (stress, fluid leakoff, etc.) will affect the fracture geometry predictions and result in a new pumping schedule to optimize the pumping schedule for the materials available for the fracturing treatment. Once this data is obtained, the invention can produce the appropriate pumping schedule based on the new well parameters instead of running simulations for multiple pumping schedules to determine which comes closest to the desired conductivity profile. This new approach can reduce the iterations required to optimize a fracturing treatment and significantly reduce the redesign process at the well site.
Accordingly, the present invention can be defined as a computer-aided well completion method, comprising: performing tests on a subterranean well to obtain data about physical properties of at least one earthen formation traversed by the well, and entering the data into a computer; determining, in the computer and in response to the data, an initial desired fracture length and conductivity for a fracture to be formed in at least one earthen formation traversed by the well; determining, in the computer and in response to the data and the initial desired fracture length and conductivity, a proppant and a fracturing fluid proposed to be pumped into the well to fracture the earthen formation; determining, in the computer, a treatment schedule for pumping the fluid and the proppant into the well; and pumping fluid and proppant into the well in accordance with at least part of the treatment schedule. This method can further comprise: measuring, in real time while pumping fluid and proppant, downhole parameters in the well; modifying, in the computer and in response to the measured downhole parameters, the treatment schedule; and continuing the pumping of fluid and proppant in accordance with the modified treatment schedule. The first-mentioned pumping fluid and proppant can be performed as part of performing a mini-frac job on the well. The determining steps can be performed using any suitable digital computer, including those that perform neural network processing. Preferably, determining the treatment schedule includes performing in the computer an economics analysis of projected resulting production versus a projected cost of performing the treatment.
Another definition of the present invention is as a method of completing a well to provide a desired hydrocarbon productivity, comprising: logging the well to obtain data used in measuring physical and mechanical properties of a subterranean formation traversed by the well; entering the data into a computer; using the data and predetermined production increase curves encoded into signals stored in the computer, defining in the computer a desired fracture length; determining, in the computer and in response to entered data, an expected fracture width; determining, in the computer and in response to the desired fracture length and expected fracture width, a desired proppant deposition; determining, in the computer and in response to predetermined data stored in the computer, a required proppant concentration; determining, in the computer and in response to entered data, a temperature in the well; determining, in the computer and in response to the determined temperature, a fracturing fluid to be pumped into the well for fracturing; running, in the computer, a reservoir simulation program and an economics model program using the determined proppant and fluid to determine a desired treatment schedule for pumping fluid and proppant into the well; and pumping fluid and proppant into the well in accordance with the treatment schedule. This can further comprise obtaining further data about the well while pumping fluid and proppant, and modifying the treatment schedule in real time so that the pumping continues in accordance with the modified treatment schedule.
Still another definition of the present invention is as a method of defining a fracturing treatment for a well, comprising: storing physical property data about a selected well in a computer also having stored therein data defining predetermined production increase relationships and predetermined proppant deposition and concentration relationships; operating the computer to automatically output, in response to the physical property data and the data defining production increase relationships and predetermined proppant deposition and concentration relationships, data defining a proposed fracture treatment schedule including a proposed proppant and fluid system; testing the proposed fracture treatment schedule in a fracture modeling program stored in the computer; and performing in the computer an economic analysis of the proposed fracture treatment schedule. This can further comprise: repeating the steps of operating, testing and performing with regard to defining at least one other fracture treatment schedule; and selecting one of the fracture treatment schedules to guide a fracturing treatment applied to the selected well.
Therefore, from the foregoing, it is a general object of the present invention to provide a novel and improved method for well completion or fracture optimization. Other and further objects, features and advantages of the present invention will be readily apparent to those skilled in the art when the following description of the preferred embodiments is read in conjunction with the accompanying drawings.